To elucidate the role of
leukotrienes (LT) in allergic
asthma in humans the effect of
MK-886, an LT biosynthesis inhibitor, was evaluated on
antigen-induced early (EAR) and late (LAR) asthmatic reactions and bronchial responsiveness to
histamine. Eight atopic men participated in a two-part, double-blind, placebo-controlled, crossover trial.
MK-886 was administered in two oral doses of 500 mg and 250 mg, 1 h before and 2 h after
allergen inhalation, respectively. Biochemical effects of
MK-886 were evaluated by the inhibition of urinary
LTE4 excretion and
calcium ionophore-stimulated
LTB4 biosynthesis in whole blood ex vivo.
MK-886 significantly inhibited the EAR by 58.4% (AUC0-3 h) and the LAR by 43.6% (AUC3-7 h) when compared with placebo (p < 0.01). There was no difference in PC20
histamine 30 h post
allergen challenge between
MK-886 and placebo (0.33 and 0.27 doubling doses, p > 0.1).
MK-886 inhibited
calcium ionophore-stimulated
LTB4 production in whole blood (54.2 +/- 25.6%) for up to 6 h post
allergen challenge.
LTE4 excretion in urine was inhibited by 51.5% during the EAR by as much as 80% during the LAR. This indicates that LT play a role in
allergen-induced asthmatic reactions in humans in vivo and that LT synthesis inhibitors such as
MK-886 should be further explored for the treatment of
asthma.